Generally, a chemical mechanical polisher (CMP) is a tool for flattening a wafer and a thin film thereon in order to reduce irregularities of the a wafer and the thin film which occur due to repeated processes of masking, etching, lining, etc. during the fabrication of semiconductor wafers.
A CMP comprises a platen onto which a grinding pad is attached, a slurry feeder for providing slurry for grinding on the grinding pad, a spindle for providing a physical grinding by holding wafers on the polishing pad by way of a polishing carrier and rotating the wafers in a contact state with the polishing pad, and a loading device for delivering the wafers transferred from a wafer cassette by a robot arm to a position of a polishing carrier head in order to load the wafers to and unload them from the polishing carrier head.
The loading device in a CMP is comprised of a loading cup which receives wafers, a driving axis for a right and left pivot movement and an ascending and descending movement of the loading cup between a platen and a spindle, and an arm connecting the loading cup to the driving axis.
However, because the loading device in a prior art is structured only to perform a right and left pivot movement and an ascending and descending movement of the loading cup about the driving axis when exchanging wafers between the polishing carrier head and the loading cup thereof before and after grinding the wafers, loading and unloading of the wafers can not be made at a normal position unless assembled positions of the polishing carrier head, the spindle, etc. are precisely matched with ascending and descending positions of the loading cup. Accordingly, in case that the position between the polishing carrier head and the loading cup is not possible to be precisely controlled within a limit of a permissible tolerance (typically, within ±0.05° considering an assembly tolerance when the degree of driving accuracy of the spindle including the polishing carrier head is within a limit of ±0.1°), loading and unloading of the wafers in itself cannot be performed, or damages to the wafers may occur due to poor loading of the wafers during a grinding process of the wafers after loading them into the polishing carrier head.
As a result, in order to perform an operation between the polishing carrier head and the loading cup at a normal position, it is required that either a separate position controlling device such as a mechanical actuator capable of controlling the positions of the respective components of the loading device needs to be installed additionally, or a permissible tolerance for a normal position between the polishing carrier head and the loading cup must be maintained within a limit of ±0.05°. In case of installing a separate position controlling device additionally is practically difficult in terms of the device structure considering the size of the loading cup or its water-proof treatment, etc. Further, the time necessary for loading and unloading of wafers takes unbearably long sot that the productivity becomes significantly lowered.
In order to solve the above problems in the prior art, the applicant of the present invention proposed a new loading device in Korean Patent Application No. 2002-0007565 where the new loading device has a vertical damping structure by a compression spring to support the bottom surface of a loading plate upwardly in a loading cup.
The loading cup of the loading device disclosed in Korean Patent Application No. 2002-0007565 (hereinafter '565 Application) has a structure where a cup plate is installed in a cup-shaped bath. A loading plate for receiving a wafer sits on the cup plate. A plurality of compression springs lie between the cup plate and the loading plate where the compression springs are dumped while ascending and descending in a vertical direction. That is, the compression springs support the bottom surface of the loading plate so to make a vacuum adhesion of the wafer being received in the loading plate toward the polishing carrier head, or perform a tilting operation for making a secure contact of the wafer between the bottom surface of the polishing carrier head and the top surface of the loading plate when detaching the vacuum-adhered wafer on the polishing carrier head onto the loading plate.
However, although the structure of the loading cup suggested in '565 Application is capable of loading and unloading wafers more stable compared with the structure of a known loading cup, it may not perform the movement of the loading plate actively in case that the position between the polishing carrier head and the loading cup is deviated from a permissible limit of tolerance of ±0.1° and thus the polishing carrier head and the loading cup are mismatched. Therefore, the structure of the loading cup suggested in '565 Application is not enough to accomplish a practical performance.